X-Ray CT Imaging Method and X-Ray CT Apparatus

1. An X-ray CT apparatus comprising: an X-ray data acquisition device configured to acquire X-ray projection data of an X-ray passed through a subject positioned between an X-ray generator and an opposite multi-row X-ray detector; a CT value adjustment device configured to obtain CT value conversion parameters with respect to each detector row of said multi-row X-ray detector, the CT value conversion parameters used in a CT value conversion process for normalizing CT values of the projection data; and an image reconstruction device configured to reconstruct a tomographic image from the projection data acquired by said X-ray data acquisition device using a three-dimensional back projection process in which the projection data acquired by said multi-row X-ray detector is used to reconstruct the tomographic image, said image reconstruction device further configured to perform the CT value conversion process to the projection data using the CT value conversion parameters prior to a three-dimensional back projection process.

2. An X-ray CT apparatus according to claim 1 , wherein said image reconstruction device is configured to perform the CT value conversion process after a reconstruction function convolution process.

3. An X-ray CT apparatus according to claim 1 , wherein said image reconstruction device is configured to perform the CT value conversion process to the projection data by using the CT value conversion parameters prior to a reconstruction function convolution process and after pre-processing.

4. An X-ray CT apparatus according to claim 1 , wherein the CT value conversion parameters are determined based on a contribution rate of the projection data of each detector row of said multi-row X-ray detector to each pixel in the tomographic image.

5. An X-ray CT apparatus comprising: an X-ray data acquisition device configured to acquire X-ray projection data of an X-ray passed through a subject positioned between an X-ray generator and an opposite multi-row X-ray detector; a CT value adjustment device configured to obtain CT value conversion parameters with respect to each detector row of said multi-row X-ray detector based on a contribution rate of the projection data of each detector row to each pixel in a tomographic image, the CT value conversion parameters used in a CT value conversion process for normalizing CT values of the projection data; and an image reconstruction device configured to reconstruct the tomographic image from the projection data acquired by said X-ray data acquisition device using a three-dimensional back project ion process in which the projection data acquired by said multi-row X-ray detector is used to reconstruct the tomographic image, said image reconstruction device further configured to perform a CT value conversion process to the projection data by using the CT value conversion parameters after a three-dimensional back projection process.

6. An X-ray CT apparatus according to claim 5 , wherein the contribution rate of the projection data of each detector row of said multi-row X-ray detector is determined by a position of an X-ray focus, a position of each detector row of said multi-row X-ray detector, a position on an x-y plane of each pixel of the tomographic image, and a z-axis coordinate position on the tomographic image, wherein a revolving plane of said X-ray data acquisition device is defined as the x-y plane, and a moving direction of an imaging table which is perpendicular to the x-y plane is defined as a z direction.

7. An X-ray CT apparatus according to claim 5 , wherein the contribution rate of the projection data of each detector row of said multi-row X-ray detector is determined by a helical pitch and a z-axis coordinate position on the tomographic image in a helical scan.

8. An X-ray CT imaging method comprising the steps of: acquiring X-ray projection data of an X-ray passed through a subject positioned between an X-ray generator and an opposite multi-row X-ray detector having a plurality of detector rows; and reconstructing a tomographic image from the projection data by executing a CT value conversion process for converting the projection data using CT value conversion parameters to normalize CT values of the projection data, the CT conversion parameters obtained with respect to each detector row of the plurality of detector rows, and using a three-dimensional back projection process in which projection data acquired by the plurality of detector rows is used to reconstruct the tomographic image.

9. An X-ray CT imaging method according to claim 8 , wherein reconstructing a tomographic image comprises performing a CT value conversion process after a reconstruction function convolution step.

10. An X-ray CT imaging method according to claim 8 , further comprising converting the projection data of the tomographic image to CT values prior to a reconstruction function convolution process and after pre-processing.

11. An X-ray CT imaging method according to claim 10 , wherein converting the projection data of the tomographic image to CT values comprises determining the CT value conversion parameters by taking into account the contribution rate of the projection data from each detector row to each pixel in a tomographic image.

12. An X-ray CT imaging method comprising the steps of: acquiring X-ray projection data of an X-ray passed through a subject positioned between an X-ray generator and an opposite multi-row X-ray detector including a plurality of detector rows; reconstructing a tomographic image from the projection data using a three-dimensional back projection process in which the projection data from the plurality of detector rows is used to reconstruct the tomographic image; and performing a conversion process on the tomographic image data after the three-dimensional back projection process, the conversion process based on CT value conversion parameters used for normalizing CT values of the projection data, the CT value conversion parameters obtained with respect to each detector row of the plurality of detector rows based on a contribution rate of the projection data of each detector row to each pixel in the tomographic image.

13. An X-ray CT imaging method according to claim 12 , further comprising determining the contribution rates based on, a position of an X-ray focus, a position of each detector row of the plurality of X-ray detector rows, a position on an x-y plane of each pixel of the tomographic image, and a z-axis coordinate position on the tomographic image, wherein a revolving plane of the X-ray generator and the X-ray detector is defined as the x-y plane, and a moving direction of an imaging table which is perpendicular to the x-y plane is defined as a z direction.

14. An X-ray CT imaging method according to claim 12 , further comprising determining contribution rates based on a helical pitch and a z-axis coordinate position on the tomographic image in a helical scan.